China is a major producer of non-ferrous metals, and ranks first in non-ferrous metal production in the world for 11 consecutive years. In the smelting process of non-ferrous metals, a large amount of SO2 flue gas containing lead, arsenic, mercury, and other heavy metal dust and fume is generated. The wet purification of flue gas in acid-making system produces a large amount of wastewater i.e. polluted acid wastewater. In the polluted acid wastewater generated from the smelting of copper, nickel and gold, arsenic is the highest in concentration and most harmful among the pollutants, and heavy metal ions such as lead, cadmium, zinc, and copper are also coexisted at the same time; in the polluted acid wastewater generated from the smelting of lead and zinc, mercury and arsenic are the main pollutants, lead and zinc are also coexisted at a high concentration, and the anions are mainly fluoride and chloride ions. It is difficult to treat the polluted acid wastewater because its complex composition, high concentration of heavy metals, large fluctuation, complex forms of heavy metals and high acidity. It is also a difficult point of the heavy metal wastewater treatment in non-ferrous smelting enterprises.
At present, domestic primary methods for the treatment of polluted acid wastewater include neutralization, vulcanization-neutralization, neutralization-iron salt co-precipitation, and treatment by membrane technology. However, they all have their own drawbacks, and the treatment results are not satisfactory. Wherein, neutralization method has low treatment cost, but it produces a large amount of residue, and it is difficult to stably achieve a standard for the treated wastewater. Although vulcanization-neutralization method reduces the amount of residue compared with neutralization-precipitation method, it still produces a large amount of neutralization residues, and results in the high hardness of water and salt accumulation due to calcium and sodium ions entering the system in the treatment process, which is not conducive to wastewater recycle. The neutralization-iron salt co-precipitation method is widely used, but it has the main problems such as large amount of residues produced, inefficient use of resources, high disposal costs of residues later, risk of secondary environmental pollution. Membrane technology can be applied to treat polluted acid wastewater, with the characteristics of low energy consumption, small footprint, relatively low cost, and have become the focus of research in recent years. Recovering the acid in the wastewater through a selective ion exchange membrane facilitates the subsequent treatment of the heavy metals in the wastewater. The methods for the treatment of heavy metal wastewater by membrane technology mainly include diffusion dialysis, electrodialysis, nanofiltration and the like. Chinese Patent application No. 201310501529.7, now publication CN103553248, relates to a method and an apparatus for recycling heavy metal polluted acid wastewater, and discloses a method for recovering waste acid by an electrodialysis device and recycling heavy metals by a vulcanization device. However, the low acidity and the high concentration of fluoride and chloride ions in the regenerated acid have limited its reuse. Chinese Patent application No. 201410786969.6, now publication CN104445095, relates to a method of purifying smelting polluted acid, and discloses a method of purifying polluted acid by diffusing dialysis, ion exchange, and multi-effect evaporation; although the high recovery of acidity could be achieved, supplement of a large amount of new water increases the volume of polluted acid to be further treated, and neutralization treatment of the low-acidity wastewater containing chlorine, fluorine and heavy metals is stilled necessary, which is not conducive to reuse. Therefore, it is an important subject in the field of environmental governance in non-ferrous metal industry to develop an efficient new process for recycling polluted acid wastewater generated from washing of smelting flue gas.